Future internal combustion engines of motor vehicles, operating, for example, on the basis of jet-directed combustion methods, have lower thermal losses due to a favorable engine efficiency factor. The dissipation power of the internal combustion engine is then often no longer sufficient for heating the passenger compartment. Diesel engines also achieve a comparatively high efficiency factor such that the thermal losses are not always sufficient particularly for heating larger vehicles. For this reason, the introduction of heat exchangers is being considered, in which the exhaust gas heats the cooling water of the internal combustion engine. Furthermore, it is possible to fall back on an air-heat exchanger as was formerly used in the known boxer engine by Volkswagen.
In many cases, the thermal energy of the exhaust gas is used to heat exhaust-gas treatment devices. Such an exhaust-gas treatment device, for example, is a catalytic converter, which on the one hand may have a certain minimum operating temperature for the catalytic function and on the other hand a certain minimum operating temperature for initiating a regeneration if it is a catalytic converter with hydrocarbon trap. Such an exhaust-gas treatment device is furthermore a particle filter, for example, which likewise must reach a minimum operating temperature for initiating the regeneration.
For guiding an exhaust gas either via the heat exchanger for implementing heating in the passenger compartment or via a bypass for heating an exhaust-gas treatment device, an adjusting device may be provided in the exhaust duct, which contains a movable valve. For reasons of emissions and safety, it may be necessary to diagnose the adjusting device.
A method and a device for operating an internal combustion engine have become known from non-prepublished German Patent Application No. DE 103 00 593, which allow for a diagnosis of an adjusting device situated in an exhaust duct without an additional sensor. The internal combustion engine contains an exhaust-gas recirculation, via which in an activated state exhaust gas is directed from the exhaust duct into an intake manifold. In at least one operating state of the internal combustion engine with an activated exhaust-gas recirculation, a first intake manifold pressure is ascertained in a first position of an element of the adjusting device and a second intake manifold pressure is ascertained in a second position of the element of the adjusting device. The functioning of the adjusting device is monitored as a function of a difference between the first and the second intake manifold pressure.
The present invention has the objective of providing a method for operating an internal combustion engine and a device for implementing the method, which allow for a simple diagnosis of an adjusting device situated in the exhaust duct of an internal combustion engine.